1. Field of the Invention
The present invention relates to a method used in a communication device in a wireless communication system, and more particularly, to a method of single-cell point-to-multipoint transmission.
2. Description of the Prior Art
3GPP in Release 12 proposes single-cell point-to-multipoint (SCPTM) service to reuse the Multimedia Broadcast Multicast Service (MBMS) structure for critical communications, such as public safety applications and general commercial applications (e.g., utility companies and railways). Note that, SCPTM service aims at providing MBMS session established on a single cell for critical communications, which is different to original MBMS design for the provision of media content in a large per-planned area (i.e. MBSFN area), where MBMS session is established on a plurality of cells.
Please refer to FIG. 1, which illustrates a schematic diagram for mapping between TMGI and G-RNTI for a SCPTM service. A user equipment (UE) could perform SCPTM reception either in idle mode or in connected mode. The UE knows a Temporary Mobile Group Identity (TMGI) for the group of interest via User Service Guide (USG). The TMGI is used to identify a SCPTM service. The eNB provides the mapping between G-RNTI and TMGI by single cell-multicast control channel (SC-MCCH). When the eNB provides the TMGI and G-RNTI mapping by SC-MCCH, the UE interesting SCPTM service could monitor the SC-MCCH to find the desired SCPTM service's TMGI and the corresponding G-RNTI mapping. Once the UE finds the desired SCPTM service's corresponding G-RNTI mapping, the UE could get the desired SCPTM service's resource information by monitoring Physical Downlink Control Channel (PDCCH) associate with the corresponding G-RNTI. Then, the UE could get the desired SCPTM service from Physical Downlink Shared Channel (PDSCH).
In addition, please refer to FIG. 2, which illustrates a schematic diagram of a MBMS session life cycle for a SCPTM service according to the prior art. In FIG. 2, a MBMS session life cycle includes “service announcement”, “session start”, “MBMS notification”, “data transfer” and “session stop”. In a word, when a MBMS session for a SCPTM service is started, the MBMS session will start the data transfer until the session stop. However, this will reduce the radio efficiency over SCPTM service because a cell has to continue data transmission of the MBMS session for the SCPTM service even there are no interested UE in its coverage.